单项选择题
A．seldom B．often C．never D．always
A．Some stamps have a flower or animal on one side. B．Along with a picture on one side, there are also some words. C．Some used stamps can be worth a lot of money. D．A stamp, when used, is worth more than a new on
A．a stepladder used to have four legs. B．it is dangerous to use tools C．a tripod is safer in a tool design D．workers are safer on production lines